Viewing instruments, such as endoscopes, are generally well known in the art. Generally, an endoscope is a medical device for insertion into a body passageway or cavity that enables an operator to view and/or perform certain surgical procedures at a site inside a patient's body. As is known, endoscopes may be either rigid or flexible, and generally include a long tubular member equipped with, for example, some type of system for transmitting images to the user, and in some cases, a working channel for a surgical instrument. The endoscope has a proximal end that remains external to the patient, from which the operator can view the site and/or manipulate a surgical instrument, and a distal end having an endoscope tip for insertion into the body cavity of the patient.
Numerous variable direction of view endoscopes have been proposed, such as the swing prism designs disclosed in U.S. Pat. No. 3,856,000 to Chikama et al., U.S. Pat. No. 4,697,577 to Forkner, U.S. Pat. No. 6,371,909 to Hoeg, et al., U.S. Pat. No. 6,500,115 to Krattiger et al., and WIPO Publication No. WO 01/22865 by Ramsbottom, as well as the pan-tilt videoendoscope design, such as is disclosed in U.S. Pat. No. 5,762,603 to Thompson. These designs rely on two mechanical degrees of freedom for changing the endoscopic line of sight, as is further explained below.
The operating principles of such a scope are illustrated schematically in FIG. 1. A variable direction of view endoscope includes an endoscope shaft 10 with a proximal end 12. Such an endoscope has a view vector 14 with an attendant view field 16 having at least two degrees of freedom 18, 20. The first degree of freedom 18 permits rotation of the view vector 14 about the longitudinal axis 22 of the shaft 10, which allows the view vector 14 to scan in a latitudinal direction 24. The second degree of freedom 20 permits rotation of the view vector 14 about an axis 26 perpendicular to the longitudinal axis 22, which allows the view vector 14 to scan in a longitudinal direction 28. A third degree of freedom 30 may also be available because it is usually possible to adjust the rotational orientation of the endoscopic image.
Referring to FIGS. 2A-B, the operating principles of a typical variable direction of view instrument—namely, a dual prism scope—are illustrated. As shown in FIG. 2A, a right-angled prism 40, housed in a spherical viewing window 32, can rotate about the axis 26, representing the second degree of freedom 20. Accordingly, the view vector 14 sweeps in the longitudinal direction 28, resulting in an effective viewing range 34. As shown in FIG. 2B, the rotatable prism 40 refracts incoming light along a path 38 to a second, non-rotating prism 42, which delivers the light to an optical relay system, housed by a hollow transmission shaft 46, along a path 44. As noted, the first prism 40 rotates about the axis 26 and can be actuated by the transmission shaft 46 via a gear 50 in order to cause the view vector 14 to scan the viewing range 34 (i.e., the plane normal to the page).
As endoscopes have become more sophisticated, they have increasingly begun to include more on-board instrumentation, such as sensors and actuators. For example, in addition to image sensors, endoscopes have been proposed that include thermal sensors and pressure sensors. Pneumatic, piezoelectric, or electromagnetic actuators are also being incorporated into endoscopes for various purposes, such as mechanical zooming, automated scope insertion, retraction, rotation, and gravity camera stabilization, such as is disclosed in U.S. Pat. No. 6,097,423 to Mattsson-Boze et al.
Actuators can also be used to change the viewing direction of a variable direction of view instrument, as is further explained herein. As endoscopes gradually become more integrated with computers, automated actuation becomes more interesting because the computers can be used to control the endoscopic viewing direction, such as in the system disclosed in U.S. Pat. No. 6,663,559 to Hale et al. Accordingly, the changing endoscopic line of sight in such variable direction of view instruments is suitable for computer control through appropriately integrated actuators.
What is desired, therefore, is an actuation system that can control motion through at least two degrees of freedom in a variable direction of view instrument. What is further desired is an actuation system that does not require a lot of space or complex construction and assembly. What is also desired is an actuation system that limits transmission backlash and the need for unnecessary support bearings.